Spark plugs can be used to initiate combustion in internal combustion engines.
Spark plugs typically ignite a gas, such as an air/fuel mixture, in an engine cylinder or combustion chamber by producing a spark across a spark gap defined between two or more electrodes. Ignition of the gas by the spark causes a combustion reaction in the engine cylinder that causes the power stroke of the engine. The high temperatures, high electrical voltages, rapid repetition of combustion reactions, and the presence of corrosive materials in the combustion gases can create a harsh environment in which the spark plug functions. This harsh environment can contribute to erosion and corrosion of the electrodes and can negatively affect the performance of the spark plug over time, potentially leading to a misfire or some other undesirable condition.
To reduce erosion and corrosion of the spark plug electrodes, various types of noble metals and their alloys—such as those made from platinum and iridium—have been used. These materials, however, can be costly. Thus, spark plug manufacturers sometimes attempt to minimize the amount of precious metals used with an electrode by using such materials only at a firing tip of the electrodes where a spark jumps across a spark gap.